This invention relates to an optical space transmission apparatus and an information transmission method for the optical space transmission apparatus, and more particularly to an optical space transmission apparatus for use to send and receive desired information using a light beam which propagates in the space. The present invention provides an optical space transmission apparatus wherein information of an operation condition is transmitted together with an information signal between transmission-side and reception-side apparatuses so that a light reception result of the light reception side of a light beam is grasped by the transmission side and the light beam is sent out with an appropriate light amount thereby to reduce the frequency of replacement of a light emitting element with a simple construction.
Conventionally, an optical space transmission apparatus sends or receives desired information to or from an apparatus of a similar type located, for example, on the roof of a building using a light beam emitted from the optical space transmission apparatus or the apparatus of the similar type and propagating in the space.
An optical space transmission apparatus of the type described can transmit or receive an information signal over a broad band by modulating a laser beam and can achieve communication with a high degree of secrecy without subject to control of the Wireless Telegraphy Act or a like law.
However, although an optical space transmission apparatus of the type described can be installed simply and readily and can assure a channel, it has the possibility that the channel may be interrupted if the attenuation of the transmission path is increased by fog, rain or the like. Therefore, an optical space transmission apparatus of the type sends out a laser beam with a large amount of light so that, even if the attenuation of the transmission path increases in this manner, the laser beam may be received with a sufficient amount of light by an apparatus of an object of communication.
However, where a laser beam is sent out with a large amount of light in this manner, a high load is imposed on a light emitting element as much, and it is necessary to replace the light emitting element frequently. Particularly where an information signal to be transmitted is a broad band signal whose transfer rate is higher than 100 Mbps, it cannot be avoided using a laser diode having a high modulation allowing frequency as a light emitting element, and in this instance, as the amount of emitted light increases, the life of the light emitting element decreases significantly. Incidentally, an optical space transmission apparatus may possibly be installed on the roof of a building or a like place from which an apparatus of an object of communication can be overlooked. Therefore, it is desired that the frequency of a maintenance operation for the light emitting element such as replacement be decreased as far as possible.
It seems a promising idea, for example, to cool such a light emitting element as described above by means of a Peltier device or the like while the light emitting element is used to prolong the life of the light emitting device. However, this complicates the construction of the apparatus.
It is an object of the present invention to provide an optical space transmission apparatus which can reduce the frequency of replacement of a light emitting element while the construction is simple.
In order to attain the object described above, according to the present invention, in an optical space transmission apparatus, information regarding an operation condition which relates to transmission of a transmission light beam or reception of a reception light beam is communicated with another optical space transmission apparatus together with an information signal.
More particularly, according to an aspect of the present invention, there is provided an optical space transmission apparatus comprising a send means for sending out a transmission light beam modulated with a predetermined information signal to another optical space transmission apparatus disposed in a spaced relationship by a predetermined distance from the optical space transmission apparatus, a reception means for receiving a transmission light beam sent out from another optical space transmission apparatus in a spaced relationship by a predetermined distance from the optical space transmission apparatus as a reception light beam and a transmission means for transmitting information of an operation condition relating to reception of the reception light beam together with the information signal to another optical space transmission apparatus.
According to another aspect of the present invention, there is provided an information transmission method for an optical space transmission apparatus comprising the steps of sending out a transmission light beam modulated with a predetermined information signal to another optical space transmission apparatus disposed in a spaced relationship by a predetermined distance from the optical space transmission apparatus, receiving a transmission light beam sent out from another information space transmission apparatus disposed in a spaced relationship by a predetermined distance from the optical space transmission apparatus as a reception light beam and transmitting information of an operation condition relating to reception of the reception light beam together with the information signal to another optical space transmission apparatus.
Since an information signal of an operation condition which relates to transmission of a transmission light beam or reception of a reception light beam is communicated between the optical space transmission apparatuses together with an information signal, the transmission side one of the optical space transmission apparatuses can grasp an operation condition of the reception side one of the optical space transmission apparatuses and send out the transmission light beam with a suitable light amount. Consequently, the transmission light beam can be prevented from being sent out with an excessively large light amount from a light emitting element. Consequently, the burden to the light emitting element can be moderated as much and the frequency of replacement of the light emitting element can be reduced with a simple construction.